1. Field of the Invention
The present invention relates to a linear ball bearing unit suitable for use as a slide bearing unit in, for example, machine tools, machining centers or the like, as well as in transportation robots having parts which make reciprocal sliding motion while carrying heavy load.
2. Description of the Prior Art
A typical known linear ball bearing unit has a bearing body which is mounted on an elongated track shaft for movement along the length of the track shaft through the medium of balls interposed therebetween and retained by a ball retainer. This known linear ball bearing unit, however, suffers from various problems as follows.
Firstly, a complicated work is required for boring return passage bores for trains of non-loaded balls in the solid portions of the bearing body, to raise the production cost uneconomically.
Secondly, the known linear ball bearing unit of the type mentioned above can bear only light load particularly in the horizontal and radial directions. This is attributable to the fact that the vertical loads acting in upward and downward directions and horizontal loads acting in the horizontal directions to the left and right, as well as radial loads acting in radial directions, are born only by trains of loaded balls arranged to run along the lower sides of lateral projections projected laterally from both lateral ends of the track shaft.
Thirdly, the height of the bearing body is increased undesirably due to the necessity of the space for loaded ball trains and non-loaded ball trains on and above the track shaft, which in turn increases the level of position of the load application point of the bearing body. The loaded ball trains on the track shaft elevates also the position of load application point of the track shaft. The elevation of the load application points of both of the track shaft and the bearing body serve to deteriorate the stability of the linear ball bearing unit.
For stabilizing the bearing unit, particularly when the level of load application point of the track shaft is high, it is necessary to lower the position of the load application point of the bearing body by decreasing the vertical thickness of the same. The reduction of thickness, however, is accompanied inevitably by a reduction in the rigidity of the bearing body itself, resulting in a smaller capacity for bearing loads particularly in the horizontal and radial directions.